Research On Low NO_x Emission Characteristics And Combustion Optimization Of High Efficiency Pulverized Coal Industrial Boiler

Coal-fired industrial boilers are one of the main sources of NO_x emissions.Clean combustion and high-efficiency has always been the goal of research by industry experts.In practical production practice,it is an economic and practical means to reduce NO_x emissions and achieve energy saving through combustion adjustment.But it is not easy to find the best operating parameters under certain operating conditions.This requires a certain mastery of NO_x emission characteristics and some optimization methods to provide guidance.We have studied the high-efficiency,low-NO_x,pulverized coal industrial boiler system that developed by our research group and a Shanghai company.The system integrates pulverized coal preparation,pulverized coal storage,pulverized coal supply,boiler body,tail flue dust treatment,fly ash concentration treatment and so on,taking the technology of clean combustion of pulverized coal as the core.Which has been applied to the production practice of the enterprise for many years.Then the work is continued on experimental study on NO_x emission characteristics and establishment of precise prediction model of boiler performance in this paper.This is of practical significance to provide guidance for the optimal operation and control of boilers qualitatively and quantitatively,laying the foundation for further low NO_x emission and energy saving.Firstly,based on the mechanism of NO_x generation in the process of pulverized coal combustion,this paper study on the characteristics of high efficiency pulverized coal industrial boiler,and analyzes its low nitrogen characteristics.The results show that air classification,high-temperature and low-oxygen combustion are the main factors that can achieve low NO_x emission in this high-efficiency pulverized coal industrial boiler.Secondly,aiming at the combustion temperature,which is a key factor influencing the NO_x generation and the burner performance,an improved combustion temperature calculation model based on equation solving method is proposed.Based on the calculation model,the influence rule of various factors on the combustion temperature of the burner is analyzed.Through the grey correlation analysis,the results show the influence degree of each influencing factor on the combustion temperature was ranked from high to low ascoal parameters,excess air coefficient,hot air temperature,coal supply amount,and proportion of heat taken away by cooling water.Then the combustion temperature regulation measures are proposed on this basis.Thirdly,the NO_x emission characteristics of the boiler outlet were experimentally studied.The results show that: The NO_x emission concentration of the boiler outlet increases with the increase of the oxygen content,the boiler load and the amount of N containing in the fuel,and decreases with the increase of the volatile content.The NO_x emission characteristic test was carried out on the burner outlet.It was verified that NO_x emission could be reduced under high temperature,low oxygen combustion and strong reducing atmosphere inside.Then,the pulverized coal combustion characteristics test was conducted.Based on the experimental data of pulverized coal combustion characteristics,the correlation analysis of each operation parameter and target index were performed from a statistical point of view,so the related degree and related direction between operation parameters and target index are clarified.Then the regression equations between target index and operation parameters are established through ridge regression analysis,on the basis of the regression equation,a multi-objective planning model is established,and the optimization interval set of each operating parameter is calculated by using the standard simple climbing method and general global optimization algorithm.The results show that the boiler load has a significant impact on the level of NO_x emission,which is the most critical factor affecting the temperature of exhaust gas.O_xygen content has a significant impact on four target indicators,which is the most critical factor affecting NO_x emission concentration,fly ash carbon content and CO emission concentration.And the opening degree of the third air door has a significant impact on the level of NO_x emissions,but has no significant impact on the other three indicators.Finally,based on the experimental data of pulverized coal combustion characteristics,a prediction model of NO_x emission and boiler thermal efficiency was established based on LS-SVM,and the hyper-parameters of LS-SVM is optimized by using simulated annealing algorithm and ten-fold cross-validation.On the basis of the LS-SVM prediction model,the algorithm of an improved fast non dominated sorting genetic with elite strategy(NSGA-II)is used to optimize the multi-objective problem of boiler combustion.The results show that the prediction model has high prediction accuracy and good optimization results.It can be applied to the actual prediction and optimization of the daily operation of the pulverized coal industrial boiler,and laid the foundation for the on-line optimization of the boiler.